This invention relates to a method and apparatus for controlling the density of a foam. Specifically, the invention relates to a method and apparatus for controlling the density of a foam on a carpet structure. In the production of carpets, such as carpets of the tufted type wherein a plurality of loops of yarn are deposited in a primary backing material, the back surface of said carpet structure is generally coated with a foam. The foam coating serves to anchor the loops of yarn in the primary backing material. The foam generally comprises a natural or synthetic latex composition or like material. Exemplary of synthetic latexes employed to bind the loops of yarn in the primary backing material are styrene/butadiene copolymer latexes.
After application of the foam coating a second woven or nonwoven backing material is generally applied to the carpet structure. Exemplary of such secondary backing materials is a woven mat of jute.
The amount of foam applied to the back of the carpet structure is most desirably the minimum amount of foam suitable for achieving a desirable degree of adhesion between the loops of yarn and the primary backing material as well as a desirable degree of adhesion between the primary backing material and the secondary backing material.
It has been found desirable to apply the material which binds the loops of yarn in the primary backing maaterial (binding material) as a foam on the back surface of the carpet structure. The binder material is applied as a foam for several reasons. First, it has been found that application of the binder material as a foam tends to inhibit penetration of the binder material onto the carpet facing. Second, the application of binder material in the form of a foam has been found to produce carpet structures having a more uniform distribution of the binder material as well as producing carpet structures with the minimum amount of binder material necessary to achieve the desired properties.
It is desirable that the density (amount of gas incorporated into the foam) of the foam be maintained at a relatively constant level. This is desirable in order to achieve the desired physical properties through application of a minimum amount of foam. Since a relatively constant thickness of foam is applied to the carpet structures, variations in the density of the foam results in a surplus of binder material being applied to the carpet structure when the density of the PG,4 foam is too great and a dearth of binder material being applied to the carpet structure when the density of the foam is below a desirable level.
In the past, the density of the foam has been controlled by visual inspection of the foam as it is applied to the carpet structure. This method of control has been found to be less than desirable. The lack of the ability to carefully control the density of the foam has necessitated the application of more than the minimum amount of foam (binder material) necessary to achieve the desirable physical properties. It is desirable to find an accurate method of controlling the density of the foam within a narrow range thus enabling the application of the minimum amount of foam necessary to achieve the desirable physical properties. It is to this goal and other related goals that the present invention is directed.
In a broader sense, the invention relates to a method and apparatus for controlling the density of a foam. Foams are employed in many uses in the fabrication and food industries. In many instances wherein foams are used, it is desirable to control the density of the foam. It is to the goal of accurately controlling the density of foams that the present invention is also directed.